214 



BOTANY OF THE LIVING PLANT 



Fig. i6i. 

 Leaf of BryophyUiim after culture on moist soil, 

 adventitious buds borne at its margins. 



The case most commonly quoted is that of Bryophylluin, one of the 

 House-Leek family, whose fleshy leaves may be induced to form buds 



in the notches of the leaf- 

 margin, by pegging them 

 down on moist soil (Fig. 

 i6i). These buds rooi: 

 themselves in the soil, and 

 as the leaf decays they 

 remain as substantive 

 plants. A similar case 

 occurs in the famihar 

 Cuckoo Flower (Carda- 

 mine pratensis). In old 

 plants the radical leaves lie along the surface of the soil, and 

 buds are formed on the upper surface, usually at the forking 

 of the veins. In Malaxis paludosa, a small native swamp Orchid, 

 minute buds appear at the tips of the leaves. Frequently 

 the adventitious bud-formation appears under some stress of 

 circumstances. But this is most evident in those cases where they 

 appear upon roots. For instance, if a Poplar or an Elm be cut down, 

 the root-system is left still alive in the soil. It contains a large supply 

 of plastic material, which it uses in the formation of buds. They 

 originate without order from the region 

 of the cambium, and rise above ground 

 as "suckers" (Fig. 162). Fruit trees, 

 such as plums, if severely pruned, also 

 produce similar suckers. These are 

 familiar objects in the vegetable garden, 

 where plums are trained against a 

 wall and pruned. Such adventitious 

 developments are clearly related to a 

 check of the aerial shoot, and may be 

 held to be a method of recovery from it. 

 A special interest attaches to the fact 

 that vegetative propagation is common 

 among alpine plants. In them vege- 

 tative buds easily detached replace flower buds. This is seen in 

 Polygonum viviparwn, where the lower part of the inflorescence bears 

 as a rule bulbils only, while a variable number of flowers occupy its 

 distal end. The rare Saxifraga cernua seldom flowers in Britain, but 

 usually bears bulbils instead. Certain Grasses frequently show this 





Fig. 162. 

 Root of Populus alba, bearing adven- 

 titious buds, which come above ground 

 as suckers. (Reduced.) 



